Subject nitrogen—hydrogen bonds

Aliphatic and cyclic amine NH protons absorb from S 3.0 to 0.5 aromatic amines absorb from S 5.0 to 3.0 in CDC13 (see Appendix E) because amines are subject to hydrogen bonding, the shift depends on concentration, solvent, and temperature. Amide, pyrrole, and indole NH groups absorb from 8 8.5 to 5.0 the effect on the absorption position of concentration, solvent, and temperature is generally smaller than in the case of amines. The nonequivalence of the protons on the nitrogen atom of a primary amide and of the methyl groups of N, /V-dimethylamides is caused by... 

Oxidative attack on a carbon-hydrogen bond of an alkyl group a to a nitrogen atom is not restricted to saturated aliphatic amines. In fact X in an X-N-CH- structural subunit can be virtually any common atomic grouping that can be found in stable organic molecules. For example, w-carbon hydrogens of Aralkyl-substituted aromatic cyclic amines (119), aryl amines (120), amides (121), amidines (122), A-nitrosodialkylamines (123), etc. are all subject to oxidative attack, carbinolamine formation, and in most cases release of an aldehyde or ketone depending on the substitution pattern (1° or 2°)... 

The hydrogen-bonding abilities of the ring nitrogen atom have also been the subject of investigation using IR spectroscopy, with proton donors such as phenol, pyrrole, and acetylenes in dilute carbon tetrachloride solution. Good correlations are observed 128-131 thus Eq. 

C - For powder diffraction data determination the key step is the generation of reliable trial structures for final refinement. The subject of the study reported here is the pharmaceutical material anhydrous theophylline (3,7-dihydro-1,3-dimethyl-l//-purine-2,6-dione), which contains both oxygen and nitrogen as possible hydrogen bond acceptor atoms. Solid-state NMR spectra of a commercial sample not only confirmed immediately that there was only one molecule in the crystallographic asymmetric unit but also produced distinctive and chemical shifts. 

Although not a subject of this chapter, Toney and coworkers have quantitated the reaction coordinate of a PLP-dependent L-alanrne racemase [15]. Despite the expectation that the cofactor provides resonance stabilization of the carbanion/enolate anion (quinonoid) intermediate derived by abstraction of the a-proton, the spectroscopic and kinetic analyses for the wild type racemase at steady-state provided no evidence for the intermediate in the reaction catalyzed by the wild type enzyme. Indeed, Toney had previously demonstrated that a kinetically competent quinonoid intermediate accumulates in the impaired R219E mutant [16] Arg 219 is hydrogen-bonded to the pyridine nitrogen of the cofactor. For the wild type racemase, the derived transition state energies for conversion of the bound enantiomers of alanine,... 

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